Investigation of Laminar Cirrus and Its Roles in the TTL Water Budget

Laminar cirrus is a unique and critical type of cloud in the Tropical Tropopause Layer (TTL) that can effectively interchange mass with water vapor (H₂O) and travel together with H₂O over multiple lifecycles. It dominates the cloud fraction in the TTL because of its extensiveness and longevity, but its formation mechanisms and roles in regulating the water budget in the TTL is not well understood. Therefore the microphysical processes is ill-parameterized in dehydration models involving freeze-drying processes. In this study, we developed a new java-based CALIPSO INteractive Digitization Interface (CINDI) to semi-autonomously identify and digitize the characteristics of laminar cirrus actually seen by Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Level-1 backscatter image at 532nm. This laminar cirrus database enables us to characterize this population of cirrus reliably. By investigating the coincident CALIOP ice water content (IWC) and H₂O measurements by the Microwave Lime Sounder (MLS) on a profile-by-profile basis, we are able to derive the H₂O–IWC relationship for laminar cirrus precisely. This relation further provides valuable constraints on the dehydration models characteristic of large-scale freeze-drying, which enables us to better quantify the total water budget in the TTL.